The present invention relates to a searchlight sonar for installation on a ship and detects an object to be searched such as a school of fish while changing the transmitting direction of ultrasonic waves.
Searchlight sonars are widely known as a kind of apparatus for detecting an object to be searched such as a school of fish under water by transmitting and receiving ultrasonic waves (for example, Patent Document 1). The searchlight sonars are sonar systems that transmit and receive an ultrasonic wave through a narrow beam by a transducer mounted on the bottom of a ship. Through one set of transmitting and receiving an ultrasonic wave, the searchlight sonars are capable of searching a predetermined angular range in a single direction, for example, a detection range of approximately six degrees out of 360 degrees all around the ship.
The searchlight sonars include a mechanism that is capable of freely changing the depression angle and the azimuth angle of the transducer, which transmits and receives ultrasonic waves. In a state in which the depression angle of the transducer is fixed, the searchlight sonars sequentially transmit and receive ultrasonic waves while turning the transducer like a searchlight around the ship by a predetermined angle at a time. In this manner, the searchlight sonars search in the water. The results of the search in the water performed as described above are sequentially displayed on a screen as detected images.